Position measuring devices are in wide use, especially for tool machines and in automation technologies. They are used to determine the absolute position of two objects that can move relative to each other. A basic distinction is made between linear and angle-measuring devices. Linear measuring devices, for example, are employed to determine the absolute position of two machine components of a tool machine that are able to move relative to each other. For this purpose, a measuring standard, e.g., in the form of a scale having a code track, is connected to one of the two objects, and a scanning unit is connected to the other, so that the extent of the motion of the two objects with respect to each other along the code track is able to be ascertained by scanning the code track.
Angle-measuring devices, also referred to as rotary encoders, are designed according to the same principle. Instead of the scale, however, a circular disk on whose periphery the code track is applied is used as measuring standard. The disk is connected to a shaft to be measured in torsionally fixed manner, whereas the scanning unit is fixedly mounted in relation thereto.
Certain conventional position measuring devices generate absolute positional values, and they include a digital, usually serial, interface for the communication with sequential electronics, e.g., a numerical control.
Optical, magnetic, inductive or capacitive scanning units may be used to generate positional signals.
In many technical application fields in which position measuring devices are used, additional peripheral units must be placed in the environment of the position measuring devices. These are, in particular, sensors for measuring operating parameters of the system at which the position measuring device is operated, such as temperature, vibration and moisture sensors. Another group of peripheral units are data storage units in which system-relevant information is stored or can be stored. Since the measured values or the information of the peripheral units are/is frequently also needed in the position measuring device, and since the position measuring device is already connected to the control via a fast serial interface as it is, the option of connecting peripheral units directly to the position measuring device was created in order to simplify the wiring of the system and to provide for the communication between control and peripheral units using an expanded interface protocol of the fast serial interface.
German Published Patent Application No. 103 06 231, for instance, describes an electronic intermediate module, to which a plurality of peripheral units can be connected and which is connected to the position measuring device via an additional interface.
In contrast, German Published Patent Application No. 10 2006 041 056 describes a position measuring device which has still further terminals for additional sensors, apart from a sensor for detecting the angle of rotation of a shaft.
The previous approaches have the disadvantage that the electrical connection of the peripheral units causes extra expense. This is true especially when the peripheral units are situated on movable units of the system.